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Downwind faster than the wind?

Old 10-20-2010, 12:09 AM
  #1  
JetPlaneFlyer
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Default Downwind faster than the wind?

So is it possible to build a wind powered vehicle that can sail directly downwind faster than the wind is blowing?

Most would say this was impossible, i know that was my initial reaction:

Take a look here: http://www.wired.com/autopia/2010/08/ddwfttw/all/1

[media]http://www.youtube.com/watch?v=LjLPPInzSzI&feature=player_embedded#[/media]!
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Old 10-20-2010, 12:18 AM
  #2  
kenchiroalpha
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Hi
Outstanding
Not isnt that something
Very interesting
Thanks for sharing that with us
Take care dear friend
Yours Hank
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Old 10-21-2010, 11:27 AM
  #3  
HX3D014
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Sounds like a hoax to me.

Let me just ask this. Will it work on a windless day if you give it a push start ?
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Old 10-21-2010, 01:42 PM
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Originally Posted by HX3D014 View Post
Sounds like a hoax to me.

Let me just ask this. Will it work on a windless day if you give it a push start ?
That's what i thought at first, but it does make sense once you get your head round it.. really it does
The blades of the prop move in a spiral path, driven by the wheels, such that the relative wind that the prop blade 'sees' always produces lift that drives the car forward.
It wouldn't work if there was no wind because it relies on the difference in velocity between the earth and the air. It's not 'eternal motion' it's wind powered and to be wind powered there has to be some wind.


Steve
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Old 10-21-2010, 06:33 PM
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Forget about all the sailing analogies. This thing is not sailing. Why it works is all in the math which I am not capable of doing. How it works is really quite simple.

Look at the pictures of this craft and imagine it sitting motionless on the desert with a strong tail wind. All but the propeller is nicely streamlined. Sitting still the propeller is the only part that is catching the wind. So this push on the motionless propeller starts the craft moving forward. Not because the wind sets it turning but just because it is fixed to the craft and catching air. Now since the propeller is geared to the wheels it starts turning and producing thrust. The wind pushes the propeller downwind. The forward motion turns the propeller and the propeller pushes back against the wind.
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Old 10-21-2010, 07:34 PM
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Originally Posted by Turner View Post
The wind pushes the propeller downwind. The forward motion turns the propeller and the propeller pushes back against the wind.
That's true until the car matches the speed of the wind.. but this vehicle went 2.8 times faster than the wind which means the wind that the car 'feels' is nearly twice as fast and coming from THE FRONT... i.e. the car is effectivly driving into a headwind.

But you are sort of correct in that due to the spiral path that the prop blades take the blade 'sees' a wind angle that's not from directly ahead but partly 'sideways'.. this allows the blade to produce lift which drives the car forward. It is very much like a yacht tacking.

Steve

Last edited by JetPlaneFlyer; 10-22-2010 at 08:54 AM. Reason: spelling
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Old 10-21-2010, 09:08 PM
  #7  
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When an airplane travels downwind the air speed and wind speed are added together to get ground speed. This is true whether the planes thrust is provided by a propeller, or a rocket. The planes thrust is determined by the output of the power unit.

With the wind car, thrust is proportional to ground speed by virtue of the prop being geared to the wheel. Like the planes above the wind is pushing against the thrust coming off the power unit which increases ground speed. As the cars speed increases more thrust comes off the prop. There is no barrier at wind speed. At wind speed, the thrust developed by the prop added to the push from the wind exceeds the power which is necessary to overcome rolling friction and all mechanical friction in the prop drive system. There is no aerodynamic drag on the fixed components of the car at wind speed. As the cars speed exceeds wind speed aerodynamic drag from the chassis becomes a factor. The cars speed will continue to increase until aerodynamic drag and frictional losses equal the combined push of prop thrust and wind speed.

I bring up the rocket to show that the whole spiral path of the propeller comparison to sailing has nothing to do with this thing working. We all know how and why propellers work and none of that changes with this application. This car works because thrust is directly proportional to ground speed and the thrust plus the push from the wind exceeds frictional losses.
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Old 10-21-2010, 10:16 PM
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I think we are maybe just looking at the 'problem' from two different perspectives. The principal of operation is in fact closely related to a boat tacking downwind, this is how the guy who designed the 'Blackbird' (Rick Carvallaro) got his inspiration and it's what he based his design on:

In 2001 a friend asked Rick Cavallaro whether a sailboat could tack downwind such that it could beat a free-floating balloon to a point directly downwind. They both knew sailboats can sail faster than the wind, but can they do well enough to beat the wind to a destination directly downwind? It would seem obvious it is not possible, but Rick knew things aren’t always as they seem. He did a quick vector analysis and convinced himself it should be possible. It certainly would be in an ice boat due to its very low drag, but could it be done with a sailboat?
As it happens, Rick’s boss at the time was legendary ocean racer and sailing navigator Stan Honey. Rick asked Stan if it had been done. Stan had recently raced PlayStation, the one boat he knew had the performance to (theoretically) do it, but Stan wasn’t sure PlayStation actually had done so.
[clip]
Rick initially took up the riddle as a thought problem. He imagined PlayStation on a broad reach and realized that if the world were a cylinder rather than a sphere with the wind blowing along its axis, the boat would trace one long spiraling path as it circled the cylindrical Earth. If racing a neutrally buoyant balloon drifting with the wind, PlayStation would get further ahead of the balloon with each rotation.
Except for scale, in this scenario PlayStation’s sail was simply the blade of a propeller. Put a second PlayStation opposite the first — on the other side of this cylindrical Earth — and you have the blades of a propeller. Rick realized it was just a matter of making a device that would constrain its prop blades to follow the same path as the two PlayStation sails. In theory this would be as simple as mounting the prop blades to a nut that can wind its way down a coarsely threaded rod. This would ensure the blades of the prop would make one foot of “sideways” movement for each foot they went downwind – just like PlayStation on a broad reach.



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Old 10-22-2010, 05:20 AM
  #9  
HX3D014
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But the wheel do not drive the Prop. The prop drives the wheels.

If it was Across wind it may be a different Cenario. but to Do it in the Down wind Direction, Nope, Aint Going to happen (Without a battery and Motor )

Steve
Forget the Ground. Just think How can it move faster than the wind if the Wind is supposed to be all that is powering it (keeping in mind A Direct with the wind Direction)

I asked will it still work if there was no wind because the wind becomes irrelevant . its just the air movement relative to the earth. and seeing as this thing was SUPPOED to have travled 2.8 times the speed of the Wind (being 15kts was it ?) then think of this, how did the ground Effect the Effiecncie, was it Benificial or a Drag problem. Now , If you reduce the Ground speed wouldnt you be Reducing that Drag Problem. And so then if this thing can do what they said it did. then even if there was no wind. once it is moving it sees the Relative wind anyway but only with a reduced Ground speed and Reduced Ground drag.


ITS a hoax lol
You can not use the winds power and Travle faster than the wind in the direction of the wind. with all componets used to harnes the wind being on the Vehicle said to travle faster than the wind


Take the Ground out of the Equation for a thought moment. Forget the wheels driving the Prop (becasue the Prop is sopposed to Drive the wheels).

Bryce
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Old 10-22-2010, 07:15 AM
  #10  
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Originally Posted by JetPlaneFlyer View Post
I think we are maybe just looking at the 'problem' from two different perspectives...
I have tried to look at it that way thinking you might be correct. I still believe there is a fundamental difference between the sailboat analogy and the Blackbird. I am working on the problem and will post it soon.
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Old 10-22-2010, 07:17 AM
  #11  
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Originally Posted by HX3D014 View Post
But the wheel do not drive the Prop. The prop drives the wheels...
No, that is incorrect. The wheels drive the prop.

These following quotes from the builders were in the comment section following the article. The emphasis is mine.

Posted by: ziploc | 08/27/10 | 10:48 pm

Two things to keep in mind:
- The wind does not turn the propeller. The wheels do.
- When the cart is up to speed, it feels a relative headwind (even though the true wind is still a tailwind).
Posted by: ziploc | 08/28/10 | 8:33 am

Nope – look at the video above that was taken by Richard Jenkins. We start from a dead stop with no assist. Also, the cart has no means to accelerate using stored energy in the prop. There’s a ratchet on the prop shaft that prevents the prop from turning the wheels.
Posted by: ThinAIrDesigns | 08/28/10 | 8:23 pm |

There are numerous ways to show mathematically that the vehicle works just fine — the one that you like will be scoffed at by others and visa versa. If you are trying to explain it however, one important thing to remember however (and you keep forgetting it) is that the prop does not provide the torque to drive the wheels, the wheels provide the torque to turn the propeller.

In answer to your question, it will not work if there is no wind because it is powered by the wind.
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Old 10-22-2010, 07:40 AM
  #12  
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Bryce,
Turner is correct.. the wheels drive the prop, which is why it wouldn’t work if you took the ground away. There needs to be a speed differential (a.k.a. wind) between air and ground. This is not eternal motion and it’s not breaking any laws of physics, it’s powered by the wind.

You might of heard of Mark Drela, professor of Aerodynamics at MIT and about the most highly respected aerodynamicist in the field of model aircraft?.. Here's what Mark had to say and his calculations to back it up: http://www.boatdesign.net/forums/boa...tml#post251760 (mark is discussing using the same idea on a boat to travel directly downwand faster than the wind, the car is easier!)

Or here's what the independent observer from the North American Land Sailing Association had to say after ratifying the world record run:http://www.nalsa.org/DownWind.html


As I said in my last post; this is no different in basic principal to what existing land yachts have been doing for ages, that’s being able to tack (zig-zag) downwind to a direct downwind target faster than the actual wind gets to that same target. Although this vehicle travels directly downwind without any zig-zag’ing the blades are in effect ‘tacking’ just like the yacht.

No, it's not a hoax, it's just difficult to understand!

Steve
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Old 10-22-2010, 12:51 PM
  #13  
HX3D014
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OK, I think I know what you are all saying.
the wind is pushing on the Props thrust, the prop is being turned by the wheel to provide the Thrust.
the More the wind pushes on the thrust the more Ground speed thus the more thrust from the Prop.

I think I am Getting it now.


........
I think ?

.......


Well I'll be a monkeys Uncle.
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Old 10-22-2010, 09:33 PM
  #14  
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Now could a glider with a big prop at the rear, traveling down wind, eventually reach Warp velocity ?.......perhaps we will soon be listening to the sonic bangs at the dynamic soaring slopes.......
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Old 10-22-2010, 09:44 PM
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Originally Posted by HX3D014 View Post
OK, I think I know what you are all saying.
the wind is pushing on the Props thrust, the prop is being turned by the wheel to provide the Thrust.
the More the wind pushes on the thrust the more Ground speed thus the more thrust from the Prop.

I think I am Getting it now.


........
I think ?

.......


Well I'll be a monkeys Uncle.

You do have it except for the last part. With constant wind speed it is the thrust that is increasing with increasing ground speed and pushing more against the wind. Good work!
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Old 10-22-2010, 11:02 PM
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Originally Posted by Turner View Post
You do have it except for the last part. With constant wind speed it is the thrust that is increasing with increasing ground speed and pushing more against the wind. Good work!
Thats what I was trying to say Here
"more Ground speed thus the more thrust from the Prop"
Thanks anyway Turner
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Old 10-23-2010, 04:47 AM
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Yes, but could you start it from a treadmill?

(sorry, couldn't resist! )
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Old 10-23-2010, 09:37 AM
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Originally Posted by FlyWheel View Post
Yes, but could you start it from a treadmill?

(sorry, couldn't resist! )
That's a good question and the answer is 'yes'. Put the Blackbird vehicle on a big treadmill that was running , lets say north. The Blackbird once up to speed would run to the south, opposite the direction of the treadmill at about 3x treadmill speed!

Ahhggggg

Steve
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Old 05-18-2011, 05:31 AM
  #19  
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Default C'mon guys, you've been duped!

Get real, it's simply impossible to use the wind's power to outrun the wind IN THE WAY YOU'RE IMAGINING (ie continuously). Once you reach the same ground speed as the wind, you have no wind left to extract power from.

Yes you have ground speed and kinetic energy, BUT: As soon as you extract kinetic energy via the wheels, you create enough drag to slow you way below wind speed. The drag from the wheels must always exceed the push from the prop. Due to frictional and efficiency losses in the system, you can't even come out even. The fancy vehicle will be slower than a feather being blown downwind. It will even be slower than the SAME vehicle without the prop! Don't be fooled by all the talk about "math" and "calculations" and "geometry". It's just as simple as it seems to be at first glance---impossible.

Except for the little lie/trick involved.

This is a sham rather than a total hoax. The vehicle can indeed go faster downwind than wind speed using only wind power. That much is true. The catch is what they're NOT saying: You can only do it for a small fraction of the time you're running the machine downwind. YOU CANNOT DO IT CONTINUOUSLY (the way a boat on tack can). You must use wind power from the past, stored up, to go faster than the wind in the present. If you run the vehicle for 5 minutes, you can outrun the wind for some small fraction of that time. However, over the total 5 min run time, the AVERAGE speed of the vehicle will be significantly slower than the average wind speed.

The way it is done is just stupid and trivial. Not at all clever or worth bothering with. They simply store energy in a battery generated by the wheels as the vehicle is carried downwind. (At this stage the vehicle MUST go slower than wind speed). It is true that this stored energy is "wind power". Once enough energy is stored we enter stage 2: stored current is directed from the battery to the ELECTRIC MOTOR behind the big prop.

The battery runs the prop, which then can push the vehicle above wind velocity until the battery runs out. All done on "wind power". SO WHAT. BIG DEAL!

The designer alludes to my explanation by describing using the wind as a "lever". Storing energy for a long period and utilizing it over a short period is simple leverage. Oh boy. Earth shattering technology.

You might as well use a stationery windmill to charge your RC car batteries, then run the car downwind 50 MPH--same result. In the case at hand, the windmill is attached to the car and energy transfer routed through the wheels (thus decreasing net efficiency) but the end result and physics are EXACTLY THE SAME. Except that this setup includes the useless contrivance designed to bamboozle everyone.

The common "upwind tack" that any sailor can do is far more complex, counterintuitive and interesting a task than the one this stupid vehicle performs. And the sailor isn't BS'ing anyone.
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Old 05-18-2011, 06:59 AM
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Sorry, no motors or batteries involved.
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Old 05-18-2011, 07:17 AM
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Sorry RZielin, you obviously didnt follow the links and/or read them closely enough.

It works quite well.

I think its brilliant!

Just finished watching a Harry Potter movie
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Old 05-18-2011, 07:43 AM
  #22  
RZielin
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Originally Posted by Turner View Post
Sorry, no motors or batteries involved.
Oh yeah? Did you look inside? If there are no motors or batteries, then there is a rocket, or a nuclear reactor, or a big rubber band, because that is the only way this thing could ever beat the wind while powered by the wind. I'm right because I HAVE TO BE RIGHT. No clever contraption can break the laws of thermodynamics.

Don't you think this guy would be a billionaire already if he could actually do what you think he claims? (He's actually more careful about his claims than posters to this thread are. He never actually claims to sustain an average speed greater than average wind speed, nor does he say there's no battery or storage device).

Given the simplicity and crudeness of his vehicle, don't you think Chris Columbus or NASA or DARPA or the Dutch or some yacht racer would have figured this out a long time ago if it was possible? They've been using wind power for a long time. Da Vinci, Keppler, Newton and Bernoulli knew quite enough about angles, vectors, props, sailing and fluid dynamics to have done this with half their cortex tied behind their backs. If only for those pesky laws of physics!

Damn, I'm sure there's a way to make my lipos put out more watts than I put in.
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Old 05-18-2011, 08:40 AM
  #23  
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RZielin,
Just because you don't understand it is not proof that something is impossible

It's not breaking the laws of thermodynamics, it's not 'over-unity' and it's not eternal motion, it's not 'getting more energy out than was put in'.... it is powered by the wind. If the wind stops the yacht stops, the energy needed to propel the yacht is always less than the energy 'harvested' from the wind, no laws of physics are being broken here.

Although the craft moves faster than the wind the blades are geared so that they still feel a wind 'behind them'.. This is similar to a land yacht tacking downwind (which BTW is also capable of outrunning the wind). The rotation of the blades works just like the sail of the yacht tacking, but it's a continuous rotary 'tack' rather than a zig-zag.

The record was independently verified by the US land yachting association (or whatever the proper name is).. it's all on the links provided previously in the posts, including detailed speed and direction recordings for both the yacht and the prevailing wind.

I can understand people struggling to grasp the concept as it's highly quite counter intuitive. But continued denial when it's been done, recorded, the physics meticulously explained, and independently verified... that i struggle to understand...

Long before they actually did it the physics was verified by, among others, Prof. Mark Drela who is a world renowned professor of aerodynamics at MIT and, among other achievements, designer if airfoils used on many of the world top sailplanes. Prof. Drela has an excellent grasp of physics I think


Was i physically there to see it you will no doubt ask?.. No i wasn't, neither was I there to see Neal Armstrong walk on the moon or the Wright brothers fly, but i accept these things occurred because of the supporting evidence and because of expert peer review.

Steve
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Old 05-19-2011, 12:57 AM
  #24  
RZielin
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Sorry, you haven't convinced me of anything. It would indeed be "over unity" to go faster than the wind. In fact, the inventor is careful NOT to make the claims you are making. He never denies the explanation that I gave, which is the only possible explanation. He alludes to "leverage" which is what I describe (the car stores wind energy, then releases it later at a faster rate to TEMPORARILY push the car faster than the wind). It cannot do the conversion continuously nor in real time. I looked at Drela's post--it makes NO claim that you describe. SHOW ME THE REFERENCE. Show me any claim from Drela or the inventor that negates what I have said.

Regarding YOUR misunderstanding: Let's try this:

Imagine a perfectly efficient wind powered car going down wind with NO frictional losses (a perfect rolling "parachute", if you will). It goes exactly AT wind speed downwind. Now, if you want to go faster, you're going to create apparent wind, aka a headwind. The only way to do that without breaking the laws of thermodynamics is to input energy into the car somehow, to overcome the resistance of the apparent wind.

ANSWER ME THIS: Where does that extra energy (to overcome headwind) come from?

You cannot say "the wind" because from the car's frame of reference, there is no longer any wind--it is experiencing dead calm (with rolling wheels). No "gearing" can make a prop spin in dead calm. At wind speed, the car's frame of reference does not include ANY wind, only kinetic energy in relation to the ground.

You could say "the car extracts the additional energy to overcome headwind from the wheels--the wheels drive the prop", but that would steal some of the energy input from the wind and make the car slow down. Putting that same energy from the wheels into the prop is still the same energy, not more. If it wasn't enough to push the car faster before, it isn't now either. No gearing can overcome that fact (it just loses more energy d/t more friction). Props are not inherently more efficient than parachutes (which is what the car is), in fact they are less efficient.

You make a patently nonsensical statement: "The energy needed to propel the yacht is always less than the energy "harvested" from the wind". Once the car is at wind speed, it cannot "harvest" ANY energy from the wind. It can only passively maintain wind speed. (In reality less due to efficiency and frictional losses). At wind speed, the prop experiences dead calm and stops spinning. The only way the car can use "harvested" wind energy is if it was stored up from the past, when the car was below wind speed and therefore the prop was spinning. That's been my claim all along.

Sorry, but you've bamboozled yourself. The only interesting thing here is WHY did the inventor bother to help you bamboozle yourself? It's a pointless exercise, except maybe to demonstrate the lack of physics understanding in America.
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Old 05-19-2011, 02:24 AM
  #25  
Larry3215
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You are confusing the speed of the car and the wind with the energy harvested from the wind. They are not the same things at all and are not tied together the way you are thinking. I had the same misconception when I first heard of this.

But, obviously you are not hear to learn anything.

Let me ask, what are your credentials, education? Im curious how they stack up against the people who have certified that this does work - like Dr Mark Drela among others?
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